Mechanical power transmission by using driving and driven pulleys with a connecting belt has long been known. A variation in this basic arrangement involves an idler pulley for supporting the belt, notwithstanding that the position of the belt may change slightly during operation of the drive.
An example of an idler pulley arrangement is shown in Shepley et al. U.S. Pat. No. 4,747,810. The Shepley arrangement mounts a pulley for rotation about a shaft. A spherical bearing is interposed between the shaft and the pulley and permits the axis of rotation of the pulley to change locus slightly, thereby permitting the pulley to responsively align its face to the orientation of a belt. That is, the pulley does not function to maintain belt alignment but rather, responds to changes in belt position and continues to support the belt in spite of such changes.
A similar arrangement is shown in Wicker et al. U.S. Pat. No. 4,098,136. In certain of the Wicker et al. arrangement, the idler pulley is mounted for rotation on a support shaft which in turn is mounted to a lever by a ball-shaped section. The ball-shaped section permits the axis of rotation of the pulley and the longitudinal axis of the support shaft (which are coincident) to be angularly changed slightly with respect to an axis of the lever. A set screw maintains the selected position. In other arrangements, the pulley rotation axis and support shaft axis can be angularly changed with respect to one another.
Yet another such arrangement is shown in Findley U.S. Pat. No. 2,349,084. In the Findley arrangement, a pulley is supported for rotation upon a support shaft, the axes of the support shaft and of pulley rotation being coincident with one another. The position of the axis may be adjusted in small increments using a pair of convex seats which are maintained in a clamped position by a bracket.
Other arrangements for affecting the position of a rotating member, e.g., an elongate roller or a pulley, are shown in McCarty et al. U.S. Pat. No. 3,359,689; Burrough et al. U.S. Pat. No. 4,092,914; Bonnamour U.S. Pat. No. 4,096,906; Glore et al. U.S. Pat. No. 4,403,454 and Hamacker U.S. Pat. No. 4,344,693.
Certain of the devices shown in the foregoing patents share common characteristics. For example, the devices shown in the McCarty et al., Burrough et al., Findley, Bonnamour, Hamacker and Glore et al. patents, and certain of those shown in the Wicker et al. patent are constructed so that the axis of the support shaft and the axis of rotation of the pulley or roller are at a locus coincident with one another for all angular positions of the pulley or roller. To put it another way, the axes of rotation and of the support shaft cannot be angularly adjusted with respect to one another.
While the device shown in the Shepley et al. patent permits the axis of the support shaft and the axis of pulley rotation to be separately positioned with respect to one another, the Shepley et al. device merely responsively self aligns to conform to irregularities in the belt. That is, the loci of the support shaft and of the pulley axis of rotation continually change during operation and may not be maintained in a fixed angular relationship.
In addition, the devices shown in the foregoing patents require a large number of parts to effect position changes in the axis of rotation of the pulley or roller.
An improved device which may be positioned to actively maintain alignment of a belt, which permits the locus of the pulley axis of rotation to be adjusted with respect to the locus of the support axis and which employs a minimum number of parts to effect changes in the locus of such axis of rotation would be an important advance in the art.